This invention relates to repair of elongated, flexible perforated strips such as tape, film and the like, and more specifically, relates to a method and apparatus for repairing damaged sprocket feed hole perforations located along the edges of such strips, particularly motion picture film strips.
Motion picture film strips, as well as numerous other types of elongated, flexible perforated strips, include rows of perforations called sprocket feed holes along one or both edges of the strips and which are engaged by the teeth of a shuttle arm or sprocket wheel of automated equipment such as projectors to drive the strips through the equipment during use. It is not uncommon for the driving teeth to tear and damage the strip in the area of the sprocket feed holes, this being particularly true in the case of commercial film strips which may be shown many times a day over long periods, and in the case of educational films which frequently are shown by inexperienced projectionists in schools and the like.
Often, the sprocket feed hole damage will become so severe that the film cannot be used, and the damaged sections of film must be either cut out or repaired in some other manner. With relatively short sections of damage, it has heretofore been the practice to simply cut out the damaged frames and splice the remaining butt sections back together using a short length of commercially available adhesive repair tape such as disclosed in U.S. Pat. No. 3,434,898. when the damage extends over many feet of film, however, it is not practical to simply cut out the damaged footage, and typically the film must be either discarded or replacement footage obtained and substituted for the damaged film portions.
While attempts have heretofore been made at repairing elongated sections of damaged film by laminating repair tape over the damaged film footage, such attempts have not proved acceptable for several reasons. For one thing, motion picture film generally shrinks when it is developed and also with age and with changes in atmospheric conditions, and the pre-punched sprocket feed holes in commercially available repair tape which normally are dimensioned to correspond with new film prior to developing, will quickly become longitudinally disaligned with the original film sprocket feed holes when applied to developed and old film. Another problem has been that in applying repair tape, each sprocket feed hole of the tape must be very accurately aligned in the direction of the width of the film with the corresponding sprocket feed hole location on the damaged film. If not accurately aligned, the repaired film may not move smoothly through a projector and may misregister in the projection gate during projection thereby causing blurred and distorted image projection.
Still a further problem with prior attempts to repair damaged film footage with conventional repair tape has been that the tape covers not only the edge portion of the film containing the sprocket feed holes, but also the entire picture frame. In covering the picture frame, the tape hinders light transmission through the frame and picture definition and clarity may be appreciably and noticably reduced. Moreover, with such a laminated composite, the film becomes less flexible and the increased stiffness can frequently cause disalignment of the film from the drive mechanism of a projector.